(1) Field of the Invention
This invention relates to a hydrogen source, more specifically to a self contained hydrogen source, which source is particularly suitable for use in man portable applications, such as, for example, fuel cell systems. The source can, however, be used in other systems that require hydrogen on demand, such as larger fuel cells, hydrogen engines or gas chromatographs.
(2) Description of Related Art
The lack of availability of a practical, high density fuel source has prevented more widespread usage of hydrogen powered fuel cell systems. Conventionally, hydrogen is stored under high pressure as a gas in a bottle or cylinder which, due to the requirements for adequate strength of containment, mean that the amount of hydrogen stored is only of the order of 2% by weight. Hydrogen can also be stored as a liquid, however it has an extremely low boiling point of ca. 20 K. so requires cryogenic containment. This again, adds bulk and weight.
An alternative to storage is in-situ hydrogen generation. Hydrogen generating systems fall into two broad classes: the generation of hydrogen from liquid or gaseous hydrocarbons, usually referred to as reformation; and hydrogen generation by the decomposition of hydrogen containing compounds. The amount of hydrogen available by weight for most in-situ hydrogen generating systems is no greater than that obtainable from a compressed gas source.
Reformation systems are not suitable for man portable applications as they are generally large and heavy due to the equipment needed for thermal management. Furthermore, the purity of hydrogen produced is low requiring subsequent clean up reactions prior to fuel cell usage.
The decomposition of hydrogen containing compounds can be further categorized; firstly, decomposition in the presence of water, referred to as hydrolysis, and secondly, decomposition by heat, or thermolysis. Both of these methods have been investigated. A reactor for the hydrolysis of metal hydrides is the subject of U.S. Pat. No. 5,702,491. Although able to produce hydrogen, this system suffers from difficulties associated with control of the hydrolysis reaction and a low hydrogen yield, with respect to the weight of the system, due to the amount of water required.
Thermal decomposition of chemical hydrides such as amine boranes, and metal borohydrides have been investigated as means for generating hydrogen. Previous patents have described the decomposition of these compounds to produce hydrogen in a ‘one shot’ non-controllable reactor (U.S. Pat. Nos. 4,315,786, 4,157,927, 4,468,263) for use with high energy chemical lasers.